The “Really expensive 3rd party software” is the way to go. That’s why it is expensive it provide real solutions for real problems.
Now if you come here to an OpenSource forum trying to find a free solution then here is my two cents:
Create a dialplan where before asking for the PII information you can stop or pause the mixmonitor(by asking the user to press a key to start the input), then start again the recording(by asking the confirmation of the user) again. Just check that it doesn’t two differents files and if so create a start UID var to share between both files and then a script to join it every X mins or when finish(?)